Prism light guide luminaire

ABSTRACT

The luminaire for a prism light guide system consists of a longitudinal hollow structure made of transparent dielectric material. The structure has inner and outer surfaces which are in octature, and at least a portion of one outer surface that has a light release mechanism. The light release mechanisms include a non-planar surface, a rough outer surface, or round corners in a corrugated outer surface. The luminaire can further include a device positioned within the hollow structure for increasing the divergence angle θ of the light. It can consist of a diffusion screen or a mirror. Some of the walls may also be covered by a reflective material to redirect any escaping light back into them.

This is a continuation application of U.S. patent application Ser. No.527,501 filed on Aug. 29, 1983, now U.S. Pat. No. 4,615,579.

BACKGROUND OF THE INVENTION

This invention is directed to luminaires for the distribution of lightinto an area, and in particular, to luminaires for use with prism lightguides.

In U.S. Pat. No. 4,260,220, which issued on Apr. 7, 1981, in the name ofLorne A. Whitehead, a prism light guide is described by which light canbe transmitted extensive distances. This system permits the lighting ofan area using a central source of light such as the sun, or some othersource which is conveniently located.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a luminaire foruse with the prism light guide system.

This and other objects of the invention are achieved in a luminairecomprising a longitudinal hollow structure made of transparentdielectric material, said structure having inner and outer surfaceswhich are in octature and wherein at least a portion of one outersurface has a light release mechanism. The release mechanism can consistof one or more of the following:

(a) a non-planar surface,

(b) a rough outer surface, or

(c) round corners in an outer corrugated surface.

In accordance with another aspect of the invention, the luminaire mayfurther include means within the hollow structure for increasing thedivergence angle θ of the light. These can include diffusion screensand/or mirrors. The mirror should not be both perpendicular to the axisof the luminaire and planar.

With regard to another aspect of the invention, the hollow structure ofthe luminaire has a rectangular cross-section formed by four walls, eachof the walls having an inner and outer surface in octature, with atleast one of the walls having a light release mechanism. In addition,the remaining walls are covered by a highly reflective material toreflect any light back through the walls.

Many other objects and aspects of the invention will be clear from thedetailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates a luminaire in accordance with the present invention;

FIG. 2 illustrates an example of a light release mechanism;

FIG. 3 illustrates a second example of a light release mechanism;

FIG. 4 is a graph showing the intensity of light released along aluminaire;

FIG. 5 is a schematic of a luminaire with a diffusion screen;

FIG. 6 is a graph of the intensity of released light in a luminaire witha diffusion screen;

FIG. 7 is a schematic of a luminaire with a mirror;

FIG. 8 is a graph of the intensity of released light in a luminaire witha mirror; and

FIG. 9 illustrates a further embodiment of a luminaire in accordancewith the present invention.

DETAILED DESCRIPTION

As described in the above noted U.S. Pat. No. 4,260,220, which isincorporated herein by reference, the prism light guide is alongitudinal hollow structure made of transparent dielectric materialwherein the walls have planar inner and outer surfaces which are inoctature. The term octature for a given section of the structure,signifies that:

(1) all of the inner surfaces of a section, i.e. the surfaces of asection in the hollow air-space are either perpendicular or parallel toone another,

(2) the outer surfaces of a section are either perpendicular or parallelto one another, and

(3) finally, the inner surfaces are at a 45° angle to the outersurfaces.

This light guide maintains a beam within its structure as long as thebeam directional angle θ is less than a predetermined maximum valuedepending on the refractive index η of the dielectric material asdetermined by the equation: ##EQU1## For an acrylic plastic with η=1.5,θ_(max) is 27.6.°

The prism light guide will, therefore, deliver a beam of light having apredetermined spatial distribution depending on the size of the guideand an angular distribution between -θ_(max) and +θ_(max). A luminaire10 for such a light guide system is illustrated in FIG. 1. The luminaire10 consists of four walls 11 made from sheets of clear dielectricmaterials wherein the inner and outer surfaces are in octature in asimilar manner as the light guide itself and with matchingcross-section. The walls 11 are fixed together at corners 12. Inaddition however, at least the walls 11 through with it is desired forthe light to be released, are made to include one or more light releasemechanisms. One release mechanism for the luminaire consists of roundcorners 21 where surfaces meet to form the outer corrugated walls 11, asshown in FIG. 2. A second release mechanism consists of non-planarsurfaces on the outer corrugated walls 11, as shown in FIG. 3. A thirdrelease mechanism consists of surface roughness on the outer corrugatedwalls 11. All of these release mechanisms allow light to be releasedfrom the luminaire 10 in a controlled manner.

When light enters one end of the luminaire 10, it is released along itslength, and therefore, the intensity of the light within the luminaire10 decreases along the length of the luminaire 10. A graph of the lightintensity in such a luminaire is shown in FIG. 4. However, it is usuallydesired to make the brightness of the light substantially constant alongthe length of the luminaire. The brightness B of the released lightalong the length of the luminaire is a function of the intensity I ofthe light in the luminaire at that point, the angular divergence θ ofthe light and the release fraction F per reflection, i.e. B∝IθF. Byincreasing the release mechanisms along the luminaire length, therelease fraction F will increase allowing B to remain constant along theluminaire length. This technique can, however, produce manufacturingproblems since these release mechanisms must vary along the length ofthe luminaire in a complex fashion.

A second technique for producing a desired brightness B profile consistsof modifying the divergence angle θ of the light in luminaire. This maybe accomplished through the use of one or more diffusion screens in theluminaire, as shown schematically in FIG. 5, or through the use ofmirrors, as shown schematically in FIG. 7. In FIG. 5, a diffusion screen51, which is made from a translucent material, is placed at the centerof the luminaire 50. The screen 51 will cause an abrupt change in thedivergence angle θ of the light passing through it in the luminaire,releasing the light with an abrupt increase in intensity as shown in thegraph of FIG. 6.

In FIG. 7, a mirror 72 is located at the end 71 of the luminaire 70.This causes the light that reaches the end 71 to be reflected and at thesame time its divergence angle θ to be increased. The brightness will,therefore, be greater at the end 71 than at the center of the luminaire70 as shown in FIG. 8. In particular, by careful choice of the degree ofincrease of the divergence angle θ, it is possible to have the samebrightness B level at both ends of the luminaire 70. Though a convexmirror 71 is shown in FIG. 7, the divergence angle θ may be increased byother types of mirror as long as the mirror is both not perpendicular tothe axis and planar.

As noted above, with respect to FIG. 1, the luminaire 10 may have one ormore of its walls 11 made from sheets of dielectric material havinginner and outer surfaces in octature, however, with release mechanisms.The remaining walls may be highly reflective due to mirrored surfaceswhich absorb some of the light, or due to prism light guide walls withthe surfaces in octature. However, by using release mechanisms in one ormore of the walls, and/or diffuse screens or mirrors in the luminaire,some of the light will escape through the prism light guide walls. Toprevent this, all of the outer surfaces through which it is not desiredto have light escape, can, as shown in FIG. 9, be covered by a surfacewhich is highly reflective and which is not a flat specular reflector,such that the reflected rays have a higher probability of passing backthrough the prism light guide wall of the luminaire. A diffusereflective material would be ideal to form such a surface. Thisluminaire 90 has three prism light guide walls 91, and one wall 92 withrelease mechanisms for releasing light 93. In addition, the three walls91 are covered with a highly reflective diffuse material 94, such asmirrors, white paint, white plastic, white paper or white fabric. Thematerial 94 will reflect any escaping light back into the luminaire 90so that it can be released through the desired surface 92.

Many modifications in the above described embodiments of the inventioncan be carried out without departing from the scope thereof and,therefore, the scope of the present invention is intended to be limitedonly by the appended claims.

What is claimed is:
 1. A luminaire for a prism light guide systemcomprising:a longitudinal hollow structure having a predeterminedcross-section for receiving along its length a beam of light having apredetermined spatial distribution and divergence angle from the lightguide system, a predetermined portion of the wall area of the hollowstructure being made of dielectric material with inner and outersurfaces which are in substantial octature; and wherein at least aportion of the dielectric material has a light release mechanism thereinsuch that light having angular distribution of less than a angle θ_(max)is released from the luminaire surface in a controlled manner.
 2. Aluminaire as claimed in claim 1 wherein the luminaire further includesmeans within the hollow structure for increasing the divergence angle ofat least a portion of the light in the beam to release that portion fromthe luminaire.
 3. A luminaire as claimed in claim 2 wherein thedivergence angle increasing means is at least one diffusion screenlocated across the hollow structure.
 4. A luminaire as claimed in claim2 wherein the divergence angle increasing means is a mirror forreflecting a portion of the beam so as to increase it divergence angleto produce substantially equal brightness at the ends of the luminaire.5. A luminaire as claimed in claim 1 wherein the hollow structure has arectangular cross-section formed by four walls for matching thecross-section of the light guide system each of the walls having aninner and outer surface in octature and at least one of the walls havinga light release mechanism.
 6. A luminaire as claimed in claim 5 whereinthe light release mechanism increases along the length of the luminiaresuch that the brightness of the released light is substantially constantalong its length.